Shape optimization of 4D-printed multi-material morphing structures for enhanced structural stability

초록

Four-dimensional (4D) printing has attracted significant attention in engineering for its ability to introduce novel functionalities into printed structures through shape-morphing. However, structural stability remains a challenge, particularly due to geometry changes under external stimuli. To address this, this study presents a shape optimization framework to maximize the stiffness of fully deployed 4D-printed, multi-material smart structures. Acrylonitrile butadiene styrene and polycarbonate/acrylonitrile butadiene styrene are used to enable sequential morphing at their respective glass transition temperatures (105 degrees C and 125 degrees C). Structural bending is achieved through controlled longitudinal and lateral printing orientations, with geometry parameterized by width values for optimization. Tangent stiffness is maximized under a volume constraint using finite element method (FEM)-based transient thermal analysis, sensitivity evaluation, and gradient-based updates. Two application cases-a self-morphing table leg and a prosthetic leg-demonstrate the method. Optimized designs achieve up to a 28.18 % increase in stiffness over initial designs. Fabricated prototypes are thermally actuated and compression-tested, showing less than 6 % deviation from FEM predictions. These results validate the proposed framework as an effective approach for improving the performance of 4D-printed, multi-material morphing structures, with potential applications in adaptive and load-bearing systems.

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